The present invention relates to a drive shaft, and more particularly to a drive shaft suitable for use as power transmission means for rolling mills.
With a rolling mill as shown in FIG. 1, a plurality of rolls B.sub.1, B.sub.2, B.sub.3, B.sub.4 arranged in a row are driven by single drive means A through drive shafts C.sub.1, C.sub.2, C.sub.3 interconnecting the drive means and the rolls. Since the spacing L between the adjacent rolls in this arrangement is very small, couplings a as shown in FIGS. 2 and 3 are usually used in the interconnecting drive shafts C.sub.1, C.sub.2, C.sub.3 to connect a drive shaft element b, a driven shaft element c and an intermediate shaft element d together.
In the case of such rolling mills, the level of the roller during rotation undergoes delicate variations, so that the shaft elements b, c, d of the drive shaft must be adapted for angular displacement. For this purpose, clearances S.sub.1 are provided between the couplings a and shaft element b, c, d fitting therein, while clearances S.sub.2 are also provided between the opposed ends of the shaft elements b, c, d. However, when the shaft elements are thus loosely fitted in the couplings, the intermediate shaft element d during the rotation of the drive shaft undergoes vibration in the direction of the rotation and oscillation in the axial direction, giving rise to wear on the surfaces of the coupling a and the shaft elements b, c, d. in fitting contact with each other. Moreover, the vibration and oscillation will be delivered to the rolls and other portions of the rolling mill, consequently reducing the accuracy of the rolling operation and causing damage to the mechanical parts early. Presumably, these problems can be overcome if the intermediate shaft element d is provided, at its opposite ends, with universal joints of the trunnion type which permit a free angular displacement, such that fitting yokes on the universal joints are connected to the drive shaft element b and to the driven shaft element c, but this arrangement renders the drive shaft excessively great in its overall length and is not usable in rolling mills in which the roll-to-roll spacing L is limited as already stated. Additionally, the drive shaft as shown in FIGS. 2 and 3 involves difficulty in providing constant lubrication to the fitting portions.